I believe the correct answer is mRNA. Dicer is a part of RNase III which leaves double stranded RNA and pre-microRNA into short double stranded RNA fragments called small interfering RNA and microRNA respectively. The Dicer facilitates the activation of RNA induced silencing complex (RISC), which are essential for RNA interference. The RISC has a catalytic component argonate, which is an endonuclease capable of degrading mRNA. siRNAs are specfic to the mRNA sequence unlike miRNAs which are not completely complementary to the mRNA sequence.
